Yes , you can be on H4 till your wife has valid H1 status. better file for change of status from H1b to H4 based on your wife H1B approval notice before your H1B or I-94 expires, fill up the form I-539 BCIS fees $140, attach your valid I-94 copy(front and back) your spouse H1b approval copy and her valid I-94 copy(front and back) attach 2-3 recent pay stubs of your wife and employer letter from your wife employer. your change of status or I-539 should reach BCIS before your I-94 expires